The present invention relates to methods of coating proppant particulates for use in subterranean formation operations.
Subterranean wells (e.g., hydrocarbon producing wells or water producing wells) are often stimulated by hydraulic fracturing treatments. In traditional hydraulic fracturing treatments, a fracturing fluid, which may also function simultaneously or subsequently as a carrier fluid, is pumped into a portion of a subterranean formation at a rate and pressure sufficient to break down the formation and create one or more fractures therein. Typically, particulate solids, such as graded sand, are suspended in a portion of the fracturing fluid and then deposited into the fractures. These particulate solids, known as “proppant particulates” or simply “proppant,” serve to prevent the fractures from fully closing once the hydraulic pressure is removed. By keeping the fractures from fully closing, the proppant particulates aid in forming conductive paths through which fluids produced from the formation may flow.
The degree of success of a fracturing operation depends, at least in part, upon fracture porosity and conductivity once the fracturing operation is complete and production is begun. Traditional fracturing operations place a large volume of proppant particulates into a fracture to form a “proppant pack” in order to ensure that the fracture does not close completely upon removing the hydraulic pressure. The ability of proppant particulates to maintain a fracture open depends upon the ability of the proppant particulates to withstand fracture closure without crushing and, therefore, is typically proportional to the strength and volume of proppant particulates placed in the fracture. The porosity of a proppant pack within a fracture is created by the interconnected interstitial spaces between abutting proppant particulates through which produced fluids may flow. Thus, it is imperative that the proppant particulates remain in place within the fracture and that the interstitial spaces between them be open such that fluids may freely flow therethrough.
One problem that may be associated with the success of a proppant pack within a fracture is obstruction of the near-wellbore region of the fracture. Proppant particulates (and other formation solids such as formation fines) deep within the fracture may flow back during stimulation and/or production and cause buildup in the proppant pack in the near-wellbore region of the fracture. The result is reduced interstitial spaces in the near-wellbore region of the proppant pack, causing a plugging effect that may substantially reduce the conductivity potential of a fracture in a subterranean formation.
A way proposed to combat such problems involves placing a resin or other tackifying agent onto the proppant particulates in order to ensure that the proppant particulates (and formation fines) remain in place once they are placed within a fracture. As used herein, the term “tackifying” in all of its forms, refers to a substance that is generally sticky to the touch. However, traditional tacky proppant may tend to gather formation fines that can stick onto the proppant and prevent neighboring proppant particulates from properly adhering to one another in the proppant pack. Therefore, a method of coating proppant particulates that does not exhibit tackifying qualities until the proppant particulates are placed at a target interval may be of benefit to one of ordinary skill in the art.